How to solve "you cannot call a method on a null-valued expression" error

You have an object declared in the function which has a undeclared value.

Explanation:

if you will make a variable of class or object in JAVA or other reference typed languages and will not assign the value to it this error occurs.

For example :

obj object;   // this line declares a object named variable of type obj class

Here it will cause same error iff i will do it like :

obj = object = new obj();